Some people use flexwatt under the tank, but that's only for heating the water contained in the substrate to raise the humidity--flexwatt won't work for a hotspot.

Instead of doing a single piece of plexi on top, I did 2 rectangles and a square so humidity holds well and I use a lamp on a dimmer for a hotspot on the perch. I would also recommend removable perches of some kind. I use pvc mounted with closet hanger type brackets so when I need to handle I can remove the whole perch and let her come off in her own time. The majority of my bites were taken from trying to remove her from a fixed perch inside the cage. Hope this helps! You should check out amazon-alliance.com too, they are a great atb resource!